Evaluating and defining the sharpness of intraocular lenses

Abstract

To evaluate the microstructure of the edges of currently available square-edged hydrophobic intraocular lenses (IOLs) in terms of their deviation from an ideal square. Berlin Eye Research Institute, Berlin, Germany. Sixteen designs of hydrophobic acrylic or silicone IOLs were studied. For each design, a +20.0 diopter (D) IOL and a +0.0 D IOL (or the lowest available plus dioptric power) were evaluated. The IOL edge was imaged under high-magnification scanning electron microscopy using a standardized technique. The area above the lateral–posterior edge, representing the deviation from a perfect square, was measured in square microns using reference circles of 40 μm and 60 μm of radius and the AutoCAD LT 2000 system (Autodesk). The IOLs were compared with an experimental square-edged poly(methyl methacrylate) (PMMA) IOL (reference IOL) with an edge design that effectively stopped lens epithelial cell growth in culture in a preliminary study. Two round-edged silicone IOLs were used as controls. The hydrophobic IOLs used, labeled as square-edged IOLs, had an area of deviation from a perfect square ranging from 4.8 to 338.4 μm² (40 μm radius reference circle) and from 0.2 to 524.4 μm² (60 μm radius circle). The deviation area for the square-edged PMMA IOL was 34.0 μm² with a 40 μm radius circle and 37.5 μm² with a 60 μm radius circle. The respective values for the +20.0 D control silicone IOL were 729.3 μm² and 1525.3 μm² and for the +0.0 D control silicone IOL, 727.3 μm² and 1512.7 μm². Seven silicone IOLs of 5 designs had area values that were close to those of the reference square-edged PMMA IOL. Several differences in edge finishing between the IOLs analyzed were also observed. There was a large variation in the deviation area from a perfect square as well as in the edge finishing, not only between different IOL designs but also between different powers of the same design. Clinically, factors such as the shrink-wrapping of the IOL by the capsule may even out or modify the influence of these variations in terms of preventing posterior capsule opacification.